Why my watch stop measuring my wrist temperature? It keep saying 1 more night

I was having the same issues and I saw someone mention in one of these forums that you have to be wearing an Apple Watch band. I tested this theory and sure enough for 2 nights it tracked. I switch back to a generic band and it didn’t. I chatted with apple and this was their response!

Hi Dongho2022,

Thanks for posting in Apple Support Communities! Since your Apple Watch is not tracking your nightly wrist temperature changes, we suggest the following:

1. Restart your Apple Watch
2. Ensure your software is updated to the latest version: Update your Apple Watch
3. Make sure that your Apple Watch fits just right: Wearing your Apple Watch

These steps can resolve the issue you're having with tracking. If it continues after 48-72 hours, we suggest contacting Apple Support to look into this further with you.

Cheers!